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"This Harbeth User Group (HUG) is the Manufacturer's own managed forum dedicated to natural sound, realisable by controlling the confounding variables between tthe microphone and the listeners' ears.

For example, the design of and interaction between the hifi amplifier and its speaker load can and potentially will alter the sound balance of what you hear. To reproduce the sounds captured by the recording microphones, as Harbeth speakers are designed to do, you would naturally select system components (sources, electronics, cables and so on) that do not color the sound before it reaches the speakers.

Identifying components for their system neutrality should, logically, start with the interpretation and analysis of their technical, objective performance, as any and every deviation from a measurably flat frequency response at any point along the serial chain from microphone to ear is very likely to cause the total system to have an audible sonic personality. That includes the contribution of the listening room itself.

HUG specialises in making complex technical matters simple to understand, aiding the identification of audio components likely to maintain a faithful relationship between the recorded sound and the sound you hear. With our heritage of natural sound, HUG cannot be really be expected to guide in the selection, approval, endorsement or even discussion of equipment that is intend to introduce a significantly personalised sound to the audio signal chain. For that you should do your own research and above all, make the effort to visit an Authorised Dealer and listen to your music at your loudness on your loudspeakers through the various electronics offered there. There is no on-line substitute for that time investment in a dealer's showroom.

If you desire to intentionally tune your system sound to your personal taste, please consider carefully how much you should rely upon the subjective opinions of strangers. Their hearing acuity and taste will be different to yours, as will be their motives and budget, their listening distance, listening loudness and listening room treatment, not necessarily leading to appropriate equipment selection and listening satisfaction for you.

Alternatively, if faithfully reproducing the sound intended by the composer, score, conductor and musicians over your speakers is your audio dream, then understanding something of the issues likely to fulfill that objective is what this forum has been helping with since 2006. Welcome!"


Jan. 2018
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Strange noises in the bluebell woods! (M40 testing outdoors)

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  • Strange noises in the bluebell woods! (M40 testing outdoors)

    Outdoors on a warm, windless day makes a great environment for carefully measuring loudspeakers. This April 2007 has been especially warm, and today is the first time this year that I've been able to set-up outside for a serious measuring session.

    Spending an afternoon in an English wood is a wonderful experience especially at this time of year when the bluebells (Hyacinthoides non scripta) are in bloom. I can't imagine what the birds and rabbits made of the test tones - you could almost hear them trying to make sense of it - but I was ever aware that I was invading their space and that they'd be there long, long after that strange man and his noises had gone.

    First I measured our BBC reference LS3/5a as I had the original BBC anechoic chamber curves to hand and it's easy to make a cross-comparison because of the distinctive response shape, then the Monitor 40 at about 4m above ground.

    A little QuickTime video I made: http://www.harbeth.co.uk/aboutus/our..._the_woods.mov

    and here is a higher resolution image (big file): http://www.harbeth.co.uk/aboutus/our...s-xroads-c.jpg (I'm told this makes a great screensaver!)


    >
    Attached Files
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  • #2
    The Anechoic Chamber - expensive and unnecessary?

    In a recent hi-fi magazine they commented that there is a picture on our C7ES-3 web page of its development using the local Village Hall as a quasi-anechoic or 'free-field' space. They write that 'other companies use huge anechoic chambers'. I'm not so sure if that really is the general position. I'll explain.

    What is an anechoic chamber used for? It is used for testing the speaker in a reflection-free environment, or at least as reflection free as possible. A 'real' anechoic chamber prevents reflections by lining all the walls, ceiling and floor with thick wedges usually made of foam several meters thick. You can imagine that not only is the cost of such a specialised building in the million dollar range but that even with thick wedges it is not possible to soak up all the sound - so, by implication, there will be reflections and the chamber will never be 100% anechoic. This will cause problems especially when measuring the low frequency response of the speaker.

    Now this in not a new problem; the measuring environment has been the bane of speaker designers for fifty years. Once, there were several anechoic chambers in the UK but the last I'm aware of (at the BBC Research Dept.) is shortly to close and the site be redeveloped for housing. It, and presumably all previous ones, didn't have enough trade/income to justify their running costs and space. So what's the alternative?

    We're trying to measure the speaker and not the [environment + speaker]. We must avoid reflections polluting the frequency response as seen by the microphone. We can tackle this in two ways: using an anechoic chamber where the reflections are minimised (by absorption) or we can make a measurement in a normal room and (theoretically) use the power of the PC to isolate the reflections from the direct sound arriving at the mic since they will appear on the screen as noticeable glitches. (A fancy word for our post-processing is 'time windowing'). We can then combine a measurement made very close to the speaker (for the low frequencies) with a windowed one made further away for the mid/high frequencies and we can create a quasi-anechoic response just as if we were in a huge chamber.

    These days in the 'post-anechoic chamber era' the designer would use his PC to make acoustic measurements on his bench in the lab amongst all the other clutter and noise you'd find there. I go to the not inconsiderable bother of actually creating some space around the speaker in the Village Hall or outside in the woods where the reflection glitches are even more dramatic and can be windowed out with confidence. Who'd build a real anechoic chamber now that we have this analytical power in our PC's? No one.

    I have been looking back over my archives to see when this near field/far-field stitching technique was first advocated and found mention of it in 1980 by HiFi News' technical expert, James Moir even in the pre-PC days. (Picture attached of his rig - I'd forgotten all about this. A very superior affair at 7m height! Dangerous too!)

    The lab-based quasi-anechoic technique is used by most speaker manufacturers these days and is also the way Stereophile magazine (to name just one) makes their speaker frequency response measurement outside their office. Stereophile Magazine measuring set-up: http://forum.stereophile.com/photopo....php/photo/135

    But beware! The application of this stitch technique is not as easy as it sounds ..... I speak from long personal experience. So, by modern standards, the luxury of hiring the Village Hall or inconvenience of setting up in the woods is actually the height of sophistication and real dedication and can give results equal to or even better than a real anechoic chamber when carefully time windowed. I see that a representative of Dolby Labs gave a paper on this subject at the AES in 2004 - see attachment.

    Wikipedia entry for anechoic chamber: http://en.wikipedia.org/wiki/Anechoic_chamber

    Background paper on the influence of the environment on speaker measurement (let alone performance): http://www.listeninc.com/files/pdf/a...requencies.pdf

    Paper explaining how good measurements can be made in ordinary rooms (with certain caveats) and modern computer based audio test equipment: http://www.listeninc.com/files/pdf/AESFreeField.pdf

    So, back to the woods we go .... it really is the best technique but rather inconvenient and needs a warm, windless, dry, quiet day! Needless to say, if you have the luxury of an existing anechoic chamber it's single biggest advantage is 24/7 operatability.

    >
    Attached Files
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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